Method, Device and System for Implementing Optimized Inter-RAT Handover

ABSTRACT

A method, device and system for implementing optimized inter-RAT handover are disclosed. In the method, a user equipment or a source network decides to prepare for a handover to a target network. A corresponding target network ID is obtained from a configured mapping between cell IDs and target IDs according to a received cell ID. Target network bearers are set up after determining an access node of the target network. The user equipment is connected to the target network after handover preparation is complete.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/776,671, filed on May 10, 2010, which is a continuation ofInternational Application No. PCT/CN2008/072987, filed on Nov. 7, 2008.The International Application claims priority to Chinese PatentApplication No. 200710169584.5, filed on Nov. 9, 2007. Theafore-mentioned patent applications are hereby incorporated by referencein their entireties.

TECHNICAL FIELD

The present invention relates to inter-RAT handover technologies, and inparticular, to a method, device and system for implementing optimizedinter-RAT handover.

BACKGROUND

Traditional telecommunications networks, especially wirelesscommunications systems such as the Global System for Mobilecommunications (GSM) and Universal Mobile Telecommunications System(UMTS) have the merits of rich services and strong network control andtherefore have been widely adopted. With the continuous development andimprovement of network technologies, higher data rates are required.But, because of limited frequency resources and abominable transportenvironments, wireless communications systems are unable to providehigher access rates. Therefore, wideband radio access becomes a keysolution for higher access rates. Wideband radio access technologiesrepresented by Wireless Local Area Network (WLAN) and WorldInteroperability for Microwave Access (WiMAX) can provide high ratewideband radio access services. They also support nomadic and mobileapplications. The access capability of a wireless communications networkis therefore much stronger. The convergence of the mobile communicationsnetwork and wideband radio access technology becomes an evolutionarytrend of telecommunications networks.

In a moving scenario of a wideband radio access network, servicecontinuity is required when a User Equipment (UE) is handed over betweendifferent access networks. Because the network prefix varies with theaccess network link, when a UE is handed over from a source network linkto a target access network link, the network prefix of the UE's InternetProtocol (IP) address in the target access network will be differentfrom the network prefix of the IP address in the source network. As aresult, in the moving scenario, routing based on a common IP networkprefix is unable to forward packets to the target access networkposition of the UE. If the UE updates its IP address during a handoverprocess, continuity of ongoing services will be impossible.

To solve the above issue, Mobility IP (MIP) is adopted so that a UE isable to keep its Home-of Address (HOA) unchanged when moving. The MIPtechnology is briefed below.

The basic principle of MIP is that one UE is associated with two IPaddresses, namely, Home-of Address (HOA) and Care-of Address (COA), sothat the UE is able to maintain its HOA when moving. The UE obtains aHOA from the home network. When the UE moves outside the home network,the UE obtains a COA of the current network from a foreign access linkmobile proxy and notifies the home link mobile proxy of the COA. Thehome link mobile proxy binds the HOA and the COA of the UE and sets up atunnel between the home link mobile proxy and the COA (foreign accesslink mobile proxy). Afterwards, the home link mobile proxy sends packetsdestined for the HOA of the UE to the COA of the UE via the tunnel so asto complete routing of the packets.

Existing telecommunications networks allow a UE to access one or morepacket data services of a Packet Data Network (PDN). The multiple packetdata services are identified by Access Point Names (APNs). APNs ofpacket data services the UE wants to access may be pre-configured in theaccess network or be provided by the UE for the access network. Theaccess network establishes the connectivity from the UE to anappropriate Packet Data Network Gateway (PDN GW) according to an APN.The PDN GW then establishes the connectivity to the appropriate PDNaccording to the APN.

For efficient management and utilization of network resources, when theUE leaves the network, it is necessary to release resources allocatedfor the UE in time, including radio channels, bearers, various tunnelsand storage, so as to increase the utilization of radio resources.

After network evolution, the UE may obtain required services through oneaccess network of three evolved network structures; after the UE entersthe network, if the UE wants to leave the current source network andenter a target network, it is necessary to hand over the UE between thethree evolved networks. The bearer in the source network must be handedover to the target network. This includes a target network bearer setupprocess and a source network bearer release process. To guarantee thecontinuity of ongoing services when the UE is in handover, with respectto handover between the three evolved networks, the followingrequirements must be met: least impact on the handovered networks, leastimpact on the UE, least coupling between handovered networks and assuredcontinuity of services.

To meet the above requirements and to offer access choices and servicediversity, it is necessary to consider a more optimized handover methodbetween evolved networks so that inter-RAT handover is completed quicklyand accurately in real time.

FIG. 1 is a schematic drawing illustrating a structure of optimizedhandover between three evolved networks in a prior art. In FIG. 1, theinterface between a home SGW and a PDN GW is S5 (not shown in thefigure) and the interface between different evolved networks is S71,where communications are based on a tunneling protocol. With the S71interface, the communications between the UE and the target network aretransparent to the source network so as to reduce the impact of thehandover on the source network and minimize the coupling between thesource network and the target network.

When implementing the present invention, however, the inventor findsthat the prior art has at least the following defect.

In the prior art, specific processes involved in optimized handover arenot decomposed. This means there is no complete mechanism or procedurefor optimized handover between evolved networks. As a result, continuityof services can not be assured during a handover process.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a method, device and systemfor implementing optimized inter-RAT handover so as to guaranteecontinuity of services in a handover process.

A method for implementing optimized inter-RAT handover can beimplemented when a UE or a source network decides to prepare for ahandover to a target network. A corresponding target network ID isobtained from a configured mapping relations between cell IDs and targetnetwork IDs according to a received cell ID. Target network bearers areset up after determining an access node of the target network. The UE isconnected to the target network after completion of handoverpreparation.

Another method for implementing optimized inter-RAT handover includesinitiating, by a UE, a connect establishing process to a target networkvia a source network when determining to prepare for a handover in thesource network. An MME of the target network receives a connect requestand establishes a connection to an SGW. The MME determines a connectionestablishing process of handover is ongoing after completing theconnection to the SGW. A resource reservation process to an access node(AN) of the target network is initiated and the UE is connected to thetarget network after completion of handover preparation.

Still another method for implementing optimized inter-RAT handoverincludes initiating, by a UE, a connection establishing process to atarget network via a source network when determining to prepare for ahandover in the source network. A bearer setup control entity initiatesa bearer setup process to the target network. An MME receives a bearersetup request from an SGW, sends a resource reservation request, andindicates an AN of the target network not to establish an air interfaceconnection. The AN of the target network receives the resourcereservation request and reserves resources. The MME receives a responsemessage from the AN of the target network and sends a response messageto the SGW. The bearer setup control entity sends a bearer setupcomplete notification to the MME after completion of bearer setup,indicating the MME that bearers are established and connects the UE tothe target network after completion of handover preparation.

Still another method for implementing optimized inter-RAT handoverincludes initiating, by a UE, a connection establishing process to atarget network via a source network when determining to prepare for ahandover in the source network, indicating a PDN GW, by an MME or a SGW,not to switch user plane uplink and downlink data paths from the sourcenetwork to the target network when a connection between the SGW and thePDN GW is setting up, and connecting, the UE to the target network aftercompletion of handover preparation, and indicating the PDN GW, by theMME or the SGW, to switch user plane uplink and downlink data paths fromthe source network to the target network.

Still another method for implementing optimized inter-RAT handoverincludes initiating, by a UE, a connection establishing process to atarget network via a source network when determining to prepare for ahandover in the source network, indicating a PDN GW when a connectionbetween a SGW and the PDN GW is setting up, by an MME or the SGW, toswitch a user plane downlink data path from the source network to thetarget network and maintain a user plane uplink data path in the sourcenetwork after determining completion of target network bearer setup, andconnecting the UE to the target network after completion of handoverpreparation, and indicating the PDN GW, by the MME or the SGW, to switchthe user plane uplink data path from the source network to the targetnetwork.

Still another method for implementing optimized inter-RAT handoverincludes initiating, by a UE, a connection establishing process to atarget network via a source network when determining to prepare for ahandover in the source network, initiating, by a PDN GW, a interactingwith a Policy and Charging Rules Function (PCRF) after receiving abearer connection request, and obtaining a Policy and Charging Control(PCC) rule corresponding to the target network, performing simultaneous,by the PDN GW, two sets of PCC rules corresponding to the source networkand the target network and initiating a bearer setup process to thetarget network, and deleting, by the PDN GW, the PCC rule correspondingto the source network when connecting the UE to the target network aftercompletion of handover preparation.

An MME device includes a receiving unit and a processing unit, where thereceiving unit is adapted to receive a cell ID and send the cell ID tothe processing unit, and the processing unit is adapted to receive thecell ID, obtain a corresponding target network ID from a configuredmapping between cell IDs and target network IDs, determine an accessnode of the target network, and send a bearer setup request to thetarget network.

A system for implementing optimized inter-RAT handover includes a sourcenetwork, an MME, an SGW, and an evolved UMTS Terrestrial Radio AccessNetwork (E-UTRAN), where the source network is adapted to receive a cellID from a UE and obtain a corresponding target network ID from aconfigured mapping between cell IDs and target network IDs according tothe cell ID and send the target network ID to the MME, the MME isadapted to receive the target network ID or obtain the correspondingtarget network ID from the configured mapping between cell IDs andtarget network IDs according to a received cell ID, determine acorresponding E-UTRAN, and set up bearers with the SGW, the SGW isadapted to set up bearers with the MME, and the E-UTRAN is adapted toset up bearers with the MME.

Another system for implementing optimized inter-RAT handover includes asource network, an MME, an SGW, and an E-UTRAN, where the source networkis adapted to receive a connect request from a UE and send the requestto the MME, the MME is adapted to receive the connect request from thesource network, set up a connection with the SGW, and after completionof the connection with the SGW, determine that a connection setupprocess of network handover is ongoing and initiate a resourcereservation process to the E-UTRAN, the SGW is adapted to set up bearerswith the MME, and the E-UTRAN is adapted to receive a resourcereservation request from the MME, reserve resources and set up bearers.

Still another system for implementing optimized inter-RAT handoverincludes a source network, an MME, an SGW, a PDN GW, and an E-UTRAN,where the source network is adapted to receive a connect request from aUE and send the request to the MME, the MME is adapted to receive theconnect request from the source network, set up bearers to the SGW,receive a bearer setup request from the SGW, send a resource reservationrequest to the E-UTRAN and indicate the E-UTRAN not to establish an airinterface connection; receive a response message from the E-UTRAN andsend a response message to the SGW, and receive a bearer setup completenotification from the SGW and complete the bearer setup, the SGW isadapted to establish a connection with the MME and send a proxy bindingupdate message to the PDN GW according to the received response; andreceive a bearer setup complete notification from the PDN GW orgenerated by itself and send the notification to the MME, the PDN GW isadapted to receive the proxy binding update message from the SGW andestablish user plane paths with the SGW; and send a bearer setupcomplete notification to the SGW, and the E-UTRAN is adapted to receivethe resource reservation message, reserve resources and set up bearers.

Still another system for implementing optimized inter-RAT handoverincludes a source network, an MME, an SGW, and a PDN GW, where thesource network is adapted to receive a connect request from a UE andsend the request to the MME, the MME is adapted to receive the connectrequest from the source network, set up bearers to the SGW, and when aconnection is established or updated between the SGW and the PDN GW,indicate the PDN GW not to switch user plane uplink and downlink datapaths from the source network to the target network; and, after the UEis connected to the target network, indicate the PDN GW to switch theuser plane uplink and downlink data paths from the source network to thetarget network, the SGW is adapted to establish a connection with theMME, establish or update the connection with the PDN GW, and send thereceived or self-generated user plane uplink and downlink data pathprocessing indication to the PDN GW; and, after the UE is connected tothe target network, indicate the PDN GW to switch the user plane uplinkand downlink data paths from the source network to the target network,and the PDN GW is adapted to establish or update the connection with theSGW, receive the user plane uplink and downlink data path processingindication, and maintain the user plane uplink and downlink data pathsin the source network; and after the UE is connected to the targetnetwork, switch the user plane uplink and downlink data paths from thesource network to the target network.

Still another system for implementing optimized inter-RAT handoverincludes a source network, an MME, an SGW, and a PDN GW, where thesource network is adapted to receive a connect request from a UE andsend the request to the MME, the MME is adapted to receive the connectrequest from the source network, set up bearers to the SGW, and when aconnection is established or updated between the SGW and the PDN GW,indicate the PDN GW to switch a user plane downlink data path from thesource network to the target network and maintain a user plane uplinkdata path in the source network; and, after handover preparation iscomplete and the UE is connected to the target network, indicate the PDNGW to switch the user plane uplink data path from the source network tothe target network, the SGW is adapted to establish a connection withthe MME, establish or update the connection with the PDN GW, and sendthe received or self-generated user plane downlink data path processingindication to the PDN GW; and, after the UE is connected to the targetnetwork, indicate the PDN GW to switch a user plane uplink data pathfrom the source network to the target network, and the PDN GW is adaptedto establish or update the connection with the SGW, receive the userplane downlink data path processing indication, switch the user planedownlink data path from the source network to the target network, andmaintain the user plane uplink data path in the source network; and,after the UE is connected to the target network, switch the user planeuplink data path from the source network to the target network.

Still another system for implementing optimized inter-RAT handoverincludes a source access gateway (source AGW), a target access gateway(target AGW), an anchor gateway (anchor GW), and a PCRF, where thesource AGW is adapted to receive a connect request from a UE and sendthe request to the target AGW, the target AGW is adapted to receive theconnect request from the source AGW and send a bearer setup request tothe anchor GW, the anchor GW is adapted to receive the bearer setuprequest, interact with the PCRF to obtain a PCC rule corresponding tothe target network, and after handover preparation is complete and theUE is connected to the target network, delete a PCC rule applicable tothe source network, and the PCRF is adapted to interact with the anchorGW to deliver the PCC rule.

Another method for implementing optimized inter-RAT handover includessending, by a UE, a connect request to a target network via a sourcenetwork when deciding to prepare for a handover in the source network,and indicating an SGW, by an MME, not to trigger a paging process withrespect to the UE upon reception of downlink data when a user planeconnection is not established with the target network.

Still another method for implementing optimized inter-RAT handoverincludes receiving, by an MME, a connect request sent by a UE andforwarded by a source network to a target network, and indicating anSGW, by the MME, not to trigger a paging process with respect to the UEupon reception of downlink data when a user plane connection is notestablished with the target network.

Another MME device includes a receiving unit, adapted to receive aconnect request sent by a UE and forwarded by a source network to atarget network, and an indicating unit, adapted to indicate an SGW notto trigger a paging process with respect to the UE upon reception ofdownlink data when a user plane connection is not established with thetarget network.

In comparison with the prior art, the embodiments of the inventionprovide the following advantages. With the method, device and system forimplementing optimized inter-RAT handover disclosed by the embodimentsof present invention, when a UE or a source network decides to preparefor the handover to a target network, an MME obtains a correspondingtarget network ID from a configured mapping between cell IDs and targetnetwork IDs according to a received cell ID and determines the accessnode of the target network; meanwhile, the MME sets up a connection tothe SGW of the target network and the MME or the SGW indicates the PDNGW not to switch user plane uplink and downlink data paths from thesource network to the target network or to switch only the user planedownlink data path from the source network to the target network; whenthe connection with the SGW is complete, the MME sends a resourcereservation request to the access node of the target network andindicates the target network not to establish an air interfaceconnection; after handover preparation is complete and the UE isconnected to the target network, the MME or SGW indicates the PDN GW toswitch the user plane uplink and downlink data paths or the user planeuplink data path from the source network to the target network. In thisway, when the UE is handed over between different access networks in anevolved network, handover performance is improved and continuity ofservices is assured. Handover becomes seamless with a better userexperience.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 is a schematic drawing illustrating a structure of optimizedhandover between three evolved networks in a prior art;

FIG. 2 is a flowchart of optimized handover from an HRPD network to anLTE network as described in SGPP TS23.402;

FIG. 3 a is a schematic drawing illustrating a first structure of asystem for implementing optimized inter-RAT handover in an embodiment ofthe invention;

FIG. 3 b is a schematic drawing illustrating a second structure of asystem for implementing optimized inter-RAT handover in an embodiment ofthe invention;

FIG. 3 c is a schematic drawing illustrating a third structure of asystem for implementing optimized inter-RAT handover in an embodiment ofthe invention;

FIG. 3 d is a schematic drawing illustrating a fourth structure of asystem for implementing optimized inter-RAT handover in an embodiment ofthe invention;

FIG. 3 e is a schematic drawing illustrating a structure of an MME in anembodiment of the invention;

FIG. 4 is a flowchart of a method for implementing optimized inter-RAThandover in a first embodiment of the invention;

FIG. 5 is another flowchart of the method for implementing optimizedinter-RAT handover in the first embodiment of the invention;

FIG. 6 is a flowchart of a method for implementing optimized inter-RAThandover in a second embodiment of the invention;

FIG. 7 is a flowchart in a third embodiment of the invention where allbearer information is transferred in one message while the interactionbetween SGW and PDN GW is based on Proxy Mobile IP (PMIP);

FIG. 8 is a flowchart in the third embodiment of the invention wherebearers are set up one by one while the interaction between SGW and PDNGW is based on PMIP;

FIG. 9 is a flowchart in the third embodiment of the invention wherebearers are set up at a time while the interaction between SGW and PDNGW is based on a GPRS Tunneling Protocol (GTP);

FIG. 10 is a flowchart in the third embodiment of the invention wherebearers are set up one by one while the interaction between SGW and PDNGW is based on GTP;

FIG. 11 is a flowchart in a fourth embodiment of the invention where atarget access gateway indicates an anchor gateway to process user planeuplink and downlink data paths respectively on two user planes;

FIG. 12 is a schematic drawing showing setting of the indicationinformation in an embodiment of the invention;

FIG. 13 is a flowchart in the fourth embodiment of the invention where atarget access gateway indicates an anchor gateway not to switch userplane uplink and downlink data paths to a target network;

FIG. 14 is another schematic drawing showing setting of the indicationinformation in an embodiment of the invention;

FIG. 15 is a flowchart in a fifth embodiment of the invention where aPCEF on an anchor GW controls PCC rules of the source/target networkduring a handover process; and

FIG. 16 is another flowchart in the fifth embodiment of the inventionwhere the PCEF on an anchor GW controls PCC rules of the source/targetnetwork during a handover process.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The technical solution of the present invention is hereinafter describedin detail with reference to the accompanying drawings. It is evidentthat the embodiments are only exemplary embodiments of the presentinvention and the present invention is not limited to such embodiments.Other embodiments that those skilled in the art obtain without creativework based on embodiments of the present invention also fall in thescope of protection of the present invention.

FIG. 2 is a flowchart of optimized handover from a High Rate Packet Data(HRPD) network to a Long Term Evolution (LTE) network. As shown in FIG.2, the handover process includes the following steps.

Step 201: A UE accesses an HRPD Access Node (HRPD AN) to make a sessionwith the HRPD network.

Step 202: The UE or the HRPD AN makes a Handover (HO) decision.

Step 203: The UE sends an Evolved Packet System Attach/Service Requestvia the HRPD AN to an MME, requesting to be attached to the targetnetwork.

Step 204: If the MME does not obtain a Mobility Management Context (MMContext) corresponding to the UE, the MME requests a Home SubscriberSystem (HSS) to authenticate the UE and establish the corresponding MMContext.

This step is optional.

Step 205: If the MME is attached to an E-UTRAN of an Evolved PacketSystem (EPS) for the first time, the MME requests location update andobtains subscription data from the HSS.

This step is optional.

Step 206: The remaining steps of the EPS Attach/Service Request processare executed.

After this step, Downlink Data (DL Data) from a PDN GW is sent to theE-UTRAN via an established bearer and buffered in the E-UTRAN.

Step 207: Upon completion of the EPS Attach/Service Request process, theMME sends a Handover to E-UTRAN Command to the UE, notifying the UE tohand the air interface over to the E-UTRAN.

Step 208: The UE receives the message, completes air interfaceconfiguration and returns a Handover Complete (HO Complete) message tothe E-UTRAN.

Step 209: The E-UTRAN receives the HO Complete message and sends aRelocation Complete message to the MME.

Step 210: The MME sends a HO Complete message to the HRPD AN, notifyingthe HRPD AN that the UE has been successfully connected to the E-UTRAN.

Step 211: The HRPD AN releases resources using a standard processdefined by HRPD.

In the above handover process, the inventor also finds the followingdefects and weaknesses.

1. At the time of handover preparation, it is necessary to buffer datain an E-UTRAN, but the process does not specify how the MME determinesthe E-UTRAN.

2. There is no detailed description of the setup of a connection betweenthe MME and the E-UTRAN.

3. It is not specified how and when S101 and S5 connections areestablished.

4. In the handover process, to guarantee service continuity, the bearerlayer handover is transparent to the service layer and therefore it isnot allowed to interrupt the transmission of uplink data, because thisis the only way to assure transparency of handover to the service layer.In the above process, however, at the time of early path switch (whichmeans, before the UE is handed over to the target network, the PDN GW isswitched to bind the target network) for handover preparation, bothuplink and downlink data will be switched to the target network so thatuplink data transmission is interrupted and as a result services areinterrupted at the service layer; lossless data transmission cannot beassured in the uplink.

5. With early path switch, the handover process does not describe how toset up a default bearer or a dedicated bearer.

6. In the case of applying Policy and Charging Control (PCC), theprocess does not consider how PCC rules are applied by a network anchorduring the handover process to implement control (such as chargingcontrol) of the source network and the target network.

In view of the above, in embodiments of the invention, when a UE ishanded over from a source network to a target network, the MME choosesthe target network according to its configuration or information carriedin a received message and establishes a connection with the targetnetwork; the SGW sets up a connection with the PDN GW and indicates thePDN GW not to switch uplink data and to buffer received downlink data;during the handover process, when the UE is still in the source network,the uplink transport path by way of the source network is not torn downand PCC control is implemented in the handover process.

In the embodiments of the invention herein, handover is described insituations where the UE is handed over to an E-UTRAN and the accessgateway of the source network, such as trusted non-3GPP networks (CDMA2000 and WiMAX) and nontrusted non-3GPP networks (WLAN and IWLAN), isreferred to as Other Access Node (Other AN).

For the above purposes, an embodiment of the invention provides a systemfor implementing optimized inter-RAT handover.

FIG. 3 a is a schematic drawing illustrating a first structure of thesystem for implementing optimized inter-RAT handover in the embodimentof the invention. As shown in FIG. 3 a, the system includes a sourcenetwork 301, an MME 302, an SGW 303 and an E-UTRAN 304, where the sourcenetwork 301 is adapted to: receive a cell ID from a UE, send thereceived cell ID to the MME 302 directly, or obtain a correspondingtarget network ID from a configured mapping between cell IDs and targetnetwork IDs according to the received cell ID, and send the targetnetwork ID to the MME 302, the MME 302 is adapted to: receive the targetnetwork ID or obtain a corresponding target network ID from a configuredmapping between cell IDs and target network IDs according to a receivedcell ID, determine a corresponding E-UTRAN 304, and set up bearers withthe SGW 303, the SGW 303 is adapted to set up bearers with the MME 302,and the E-UTRAN 304 is adapted to set up bearers with the MME 302.

In practice, the system for implementing optimized inter-RAT handovershown in FIG. 3 a may include the source network 301, adapted to:receive a connect request from the UE and forward the request to the MME302, the MME 302, adapted to: receive the connect request from thesource network 301, set up a connection with the SGW 303, and aftercompletion of the connection with the SGW 303, decide a connection setupprocess of network handover is ongoing and send a resource reservationrequest to the E-UTRAN 304, the SGW 303, adapted to establish aconnection with the MME 302, and the E-UTRAN 304, adapted to: receivethe resource reservation request from the MME 302, reserve resources andset up bearers.

In practice, the system for implementing optimized inter-RAT handovershown in FIG. 3 a may also include the source network 301, adapted to:receive a connect request from the UE and forward the request to the MME302, the MME 302, adapted to: receive the connect request from thesource network 301, set up bearers to the SGW 303 and indicate the SGW303, and set up bearers to the E-UTRAN 304, the SGW 303, adapted to:establish a connection with the MME 302 and according to the receivedindication, if a user plane bearer to the E-UTRAN 304 is notestablished, buffer received downlink data without paging the UE, andthe E-UTRAN 304, adapted to set up bearers with the MME 302.

FIG. 3 b is a schematic drawing illustrating a second structure of thesystem for implementing optimized inter-RAT handover in the embodimentof the invention. As shown in FIG. 3 b, the system includes a sourcenetwork 311, an MME 312, an SGW 313, a PDN GW 314 and an E-UTRAN 315,where the source network 311 is adapted to: receive a connect requestfrom the UE and forward the request to the MME 312, the MME 312 isadapted to: receive the connect request from the source network 311, setup bearers to the SGW 313, receive a bearer setup request from the SGW313, send a resource reservation request to the E-UTRAN 315 and indicatethe E-UTRAN 315 not to establish an air interface connection; receive aresponse message from the E-UTRAN 315 and send a response message to theSGW 313; receive a bearer setup complete notification from the SGW 313and complete bearer setup, the SGW 313 is adapted to: establish aconnection with the MME 312 and send a proxy binding update message tothe PDN GW 314 according to the received response; receive a bearersetup complete notification from the PDN GW 314 or generated by itselfand send the notification to the MME 312, the PDN GW 314 is adapted to:receive the proxy binding update message from the SGW 313 and establishuser plane paths with the SGW 313; and send the bearer setup completenotification to the SGW 313, and the E-UTRAN 315 is adapted to: receivethe resource reservation message, reserve resources and set up bearers.

FIG. 3 c is a schematic drawing illustrating a third structure of thesystem for implementing optimized inter-RAT handover in the embodimentof the invention. As shown in FIG. 3 c, the system includes a sourcenetwork 321, an MME 322, an SGW 323 and a PDN GW 324, where the sourcenetwork 321 is adapted to: receive a connect request from the UE andforward the request to the MME 322, the MME 322 is adapted to: receivethe connect request from the source network 321, set up bearers to theSGW 323, and when a connection is established or updated between the SGW323 and the PDN GW 324, indicate the PDN GW 324 not to switch user planeuplink and downlink data paths from the source network 321 to the targetnetwork. After the UE is connected to the target network, indicate thePDN GW 324 to switch the user plane uplink and downlink data paths fromthe source network 321 to the target network, the SGW 323 is adapted to:establish a connection with the MME 322, establish or update theconnection with the PDN GW 324, and send the received or self-generateduser plane uplink and downlink data path processing indication to thePDN GW 324; and, after the UE is connected to the target network,indicate the PDN GW 324 to switch the user plane uplink and downlinkdata paths from the source network 321 to the target network, and thePDN GW 324 is adapted to: establish or update the connection with theSGW 323, receive the user plane uplink and downlink data path processingindication, and maintain the user plane uplink and downlink data pathsin the source network 321; and, after the UE is connected to the targetnetwork, switch the user plane uplink and downlink data paths from thesource network 321 to the target network.

In practice, the system for implementing optimized inter-RAT handovershown in FIG. 3 c may also include the MME 322, adapted to: receive theconnect request from the source network 321, set up bearers to the SGW323, and when a connection is established or updated between the SGW 323and the PDN GW 324, indicate the PDN GW 324 to switch the user planedownlink data path from the source network 321 to the target network andmaintain the user plane uplink data path in the source network 321; and,after handover preparation is complete and the UE is connected to thetarget network, indicate the PDN GW 324 to switch the user plane uplinkdata path from the source network 321 to the target network, the SGW323, adapted to: establish a connection with the MME 322, establish orupdate the connection with the PDN GW 324, and send the received orself-generated user plane downlink data path processing indication tothe PDN GW 324; and, after the UE is connected to the target network,indicate the PDN GW 324 to switch the user plane uplink data path fromthe source network 321 to the target network, and the PDN GW 324,adapted to: establish or update the connection with the SGW 323, receivethe user plane downlink data path processing indication, and switch theuser plane downlink data path from the source network 321 to the targetnetwork, and maintain the user plane uplink data path in the sourcenetwork 321; and, after the UE is connected to the target network,switch the user plane uplink data path from the source network 321 tothe target network.

FIG. 3 d is a schematic drawing illustrating a fourth structure of thesystem for implementing optimized inter-RAT handover in the embodimentof the invention. As shown in FIG. 3 d, the system includes a sourceaccess gateway 331, a target access gateway 332, an anchor gateway 333,and a PCRF 334, where the source access gateway 331 is adapted to:receive a connect request from a UE and forward the request to thetarget access gateway 332, the target access gateway 332 is adapted to:receive the connect request from the source gateway 331 and send abearer setup request to the anchor gateway 333, the anchor gateway 333is adapted to: receive the bearer setup request, interact with the PCRF334 to obtain a PCC rule applicable to the target network, enforcecharging rules of two sets of PCC rules, and after the handoverpreparation is complete and the UE is connected to the target network,delete the PCC rule applicable to the source network 331, in practice,the anchor gateway 333 may be PDN GW, and the PCRF 334 is adapted tointeract with the anchor gateway 333 to deliver a PCC rule.

FIG. 3 e is a schematic drawing illustrating a structure of an MMEaccording to an embodiment of the invention. As shown in FIG. 3 e, theMME device includes a receiving unit 341 and a processing unit 342,where the receiving unit 341 is adapted to: receive a cell ID andforward the cell ID to the processing unit 342, and the processing unit342 is adapted to: receive the cell ID, obtain a corresponding targetnetwork ID from a configured mapping between cell IDs and target networkIDs, determine an access node of the target network, and send a bearerestablish request to the target network.

Five embodiments will be described to explain a method for implementingoptimized inter-RAT handover provided by the present invention.

FIRST EMBODIMENT

This embodiment describes how an MME chooses an Evolved Base Node (ENB)when a UE is handed over from the other AN to an E-UTRAN.

When a UE is handed over from the other AN to an E-UTRAN, the MME maychoose an ENB in two optional solutions.

Solution 1: The other AN configures or obtains information of themapping between cell IDs and target IDs of the E-UTRAN, and when ahandover decision is made, the other AN determines the appropriatetarget ID according to the cell ID and sends the target ID in a tunnelmessage to an MME via the S101 interface; the MME receives the target IDand chooses an ENB according to the target ID.

Solution 2: The MME configures or obtains information of the mappingbetween cell IDs and target IDs; a UE or the other AN sends a cell ID ina tunnel message to the MME via the S101 interface; the MME determinesthe appropriate target ID according to the received cell ID and choosesthe corresponding ENB.

FIG. 4 is a flowchart of the method for implementing optimized inter-RAThandover in the first embodiment of the invention. In this embodiment,the mapping between cell IDs and target IDs is configured in an other ANand the other AN sends the target ID to the MME. As shown in FIG. 4, theprocess includes:

Step 401: The UE or other AN makes a handover decision.

In this step, the other AN may obtain an appropriate target ID from theconfigured mapping between cell IDs and target IDs according to aselected cell ID.

Step 402: The UE sends a Message Z carrying a connect request to theother AN.

In this step, the Message Z sent from the UE to the other AN is definedin the HRPD network and intended to initiate a connection to theE-UTRAN.

Step 403: The other AN sends a Direct Transfer message to the MME.

In this step, if a target ID is not determined in step 401, the other ANobtains the appropriate target ID from the configured mapping betweencell IDs and target IDs according to the selected cell ID. The DirectTransfer message carries the target ID.

Step 404: The MME requests authentication and location update, obtainssubscription data, and establishes an appropriate MM Context.

Step 405: The MME chooses an appropriate SGW and sends a bearer setuprequest to the SGW.

In this step, the SGW may also send a bearer setup request to the PDNGW.

Step 406: The MME chooses the appropriate E-UTRAN according to thetarget ID carried in the received Direct Transfer message.

In practice, step 406, step 405 and step 404 may be carried out inrandom order. Step 406 may perform before step 405 or before step 404;step 405 may precede step 404 and after the E-UTRAN is chosen, step 407can follow.

Step 407: The MME sets up a connection to the chosen E-UTRAN.

Step 408: The remaining steps of the handover process from the other ANto the E-UTRAN are completed.

FIG. 5 is another flowchart of the method for implementing optimizedinter-RAT handover in the first embodiment of the invention. In thisembodiment, the mapping between cell IDs and target IDs is configured onthe MME and the UE or other AN sends cell ID information to the MME. Asshown in FIG. 5, this handover process is different from the processshown in FIG. 4 in the following steps:

Step 503: The other AN sends a Direst Transfer message carrying a chosencell ID to the MME.

Step 506: The MME obtains the appropriate target ID from the configuredmapping between cell IDs and target IDs according to the cell ID carriedin the received Direct Transfer message and chooses the appropriateE-UTRAN according to the target ID.

SECOND EMBODIMENT

This embodiment deals with the specific process of establishing aconnection with the E-UTRAN after the MME chooses the appropriateE-UTRAN.

If, after choosing and obtaining SGW information, the MME finds aconnection is not established to the chosen ENB with respect to the UEand decides the current process as a connection setup process ofhandover, the MME initiates a connection to the ENB and completesconfiguring the user plane uplink bearer and the security mode.

FIG. 6 is a flowchart of the method for implementing optimized inter-RAThandover in the second embodiment of the invention. In this embodiment,the MME initiates a connection with the E-UTRAN after it chooses theappropriate E-UTRAN. As shown in FIG. 6, the process includes:

Step 601: The UE or network makes a handover decision.

Step 602: The UE sends a connect request to the MME via the other AN.

In this step, the other AN transparently transmits the connect message.

Step 603: The MME requests authentication and location update, obtainssubscription data, and establishes an appropriate MM Context.

Step 604: The MME chooses an appropriate SGW and sends a bearer setuprequest to the SGW.

In this step, the SGW may also send a bearer setup request to the PDNGW.

Step 605: The MME chooses an appropriate E-UTRAN according to thereceived target ID.

Step 606: The MME chooses the E-UTRAN and makes judgments.

In this step, after the MME chooses the E-UTRAN, the MME checks whetherthe following conditions are met:

-   1. A connection setup process of handover is ongoing;-   2. A connection is already established between the SGW and the MME;    and-   3. The MME does not establish a connection to the chosen E-UTRAN    with respect to the UE.

If the three conditions are met, the MME sends a Resource ReservationRequest to the E-UTRAN, carrying SGW information, UE capabilityparameters and security mode parameters.

Step 607: The E-UTRAN returns a Resource Reservation Response.

In this step, the E-UTRAN chooses algorithms for Radio Resource Control(RRC) encryption, integrity protection and user plane encryption anddetermines RRC related configuration information according to thereceived Resource Reservation Request; then, the E-UTRAN returns theResource Reservation Response to the MME. The response message carriesinformation of the chosen E-UTRAN such as the Tunnel Endpoint Identity(TEID) of the E-UTRAN and a handover command which includes RRCconfiguration information and chosen security parameters.

Step 608: The remaining steps of the handover process from the other ANto the E-UTRAN are completed.

THIRD EMBODIMENT

In this embodiment, dedicated bearers may be established in two schemes:

Scheme 1: Dedicated bearers are set up one by one; after the defaultbearer is set up, the bearer setup control entity where the network sidePolicy and Charging Enforcement Function (PCEF) resides, such as the SGWor PDN GW, initiates a one-by-one dedicated bearer setup process; theMME processes the received bearer setup message and indicates theE-UTRAN not to initiate an air interface bearer setup process by sendinga message or adding an indication parameter to the message.

Scheme 2: Dedicated bearer information is transferred in a message;information of a requested bearer is carried in the message and adedicated bearer is set up after a round trip of the message; and theresponse message carries information of success or failure in setting upthe dedicated bearer.

FIG. 7 is a flowchart in the third embodiment of the invention where allbearer information is transferred in one message while the interactionbetween SGW and PDN GW is based on PMIP. As shown in FIG. 7, the processincludes:

Step 701: The MME sends a bearer setup message to the SGW, carrying anindication notifying the SGW that a connection setup process of handoveris ongoing.

Step 702: The SGW receives the bearer setup message and initiates anIP-CAN Modification process to the PCRF. During the interaction, the SGWsends the appropriate IP-CAN Type to the PCRF.

This step is optional.

Step 703: The SGW receives a PCC rule returned by the PCRF anddetermines it is necessary to reserve resources for all bearers; the SGWsends a bearer setup response to the MME, carrying information of allreserved bearers.

In this step, bearer information includes TEID information.

Step 704: The MME sets up bearers with the E-UTRAN.

In this step, the established bearers may include the default bearer anddedicated bearers.

Step 705: The MME sends a bearer update message to the SGW, carryinginformation of the bearers established by the E-UTRAN, including bearersetup success information and bearer setup failure information.

Step 706: The SGW sends a Proxy Binding Update (PBU) message to the PDNGW to establish a user plane path.

This step is optional. This step is required only when it is necessaryto switch the user plane downlink data path to the E-UTRAN in advance.The PBU message or an extended parameter in the PBU message indicatesthe PDN GW to switch the user plane downlink data path to the E-UTRANand maintain the user plane uplink data path in the HRPD network. Theindication may be sent by the MME or directly by the SGW, or regeneratedby the SGW.

Step 707: The PDN GW interacts with the PCRF.

This step is optional. The PDN GW obtains the PCC rule by interactingwith the PCRF.

Step 708: The PDN GW returns a Proxy Binding Acknowledge (PBA) to theSGW.

This step is optional. The user plane path from the PDN GW to the SGWand to the E-UTRAN is connected. If the E-UTRAN receives downlink data,the E-UTRAN bufferes the downlink data.

Step 709: The SGW sends a bearer setup complete notification to the MME,indicating the MME that the bearer setup is complete via an indicationparameter or a special message.

In this step, the indication parameter is an indication parametercarried in the bearer setup complete notification message; the specialmessage is the bearer setup complete notification message.

After the UE is successfully to the target network, the SGW indicatesthe PDN GW to switch the user plane uplink and downlink data paths tothe E-UTRAN via the PBU or extended PBU message. The indication may besent by the MME or directly by the SGW, or regenerated by the SGW.

FIG. 8 is a flowchart in the third embodiment of the invention wherebearers are set up one by one while the interaction between SGW and PDNGW is based on PMIP. As shown in FIG. 8, the process includes:

Step 801: The MME sends a bearer setup message to the SGW, carrying anindication notifying the SGW that a connection setup process of handoveris ongoing.

Step 802: The SGW receives the bearer setup message and initiates anIP-CAN Modification process to the PCRF. During the interaction, the SGWsends the appropriate IP-CAN Type to the PCRF.

This step is optional.

Step 803: The SGW receives a PCC rule returned by the PCRF anddetermines it is necessary to reserve resources for all bearers; the SGWsends a bearer setup response to the MME, carrying information of thedefault bearer.

In this step, default bearer information includes TEID information.

Step 804: The MME sets up the default bearer with the E-UTRAN.

Step 805: The MME sends a bearer update message to the SGW, carryinginformation of the default bearer established by the E-UTRAN.

STEP 806: The SGW returns a bearer update response message to the MME.

Step 807: The SGW sends a dedicated bearer setup request to the MME,requesting setup of a dedicated bearer.

In this step, the SGW may send multiple dedicated bearer setup requeststo the MME in parallel so as to set up multiple dedicated bearers.

Step 808: The MME notifies the E-UTRAN to set up a dedicated bearer, andthe notification message carries information indicating the E-UTRAN notto set up an air interface connection; the indication may be a messagesent by the MME to the E-UTRAN or an extended indication parametercarried in the message sent by the MME to the E-UTRAN.

Step 809: The E-UTRAN sends a dedicated bearer setup response to theMME.

Step 810: The MME sends a dedicated bearer setup response to the SGW,carrying information of the dedicated bearer established by the E-UTRAN.

Step 811: When it is determined that all dedicated bearers areestablished, the SGW sends a PBU message to the PDN GW to set up a userplane path.

This step is optional. This step is required only when it is necessaryto switch the user plane downlink data path from the HRPD network to theE-UTRAN in advance. The PBU message or an extended parameter in the PBUmessage indicates the PDN GW to switch the user plane downlink data pathto the E-UTRAN and maintain the user plane uplink data path in the HRPDnetwork. The indication may be sent by the MME or directly by the SGW,or regenerated by the SGW.

Step 812: The PDN GW interacts with the PCRF.

This step is optional. The PDN GW obtains the PCC rule by interactingwith the PCRF.

Step 813: The PDN GW sends a PBA message to the SGW.

This step is optional. The user plane path from the PDN GW to the SGWand to the E-UTRAN is connected. If the E-UTRAN receives downlink data,the E-UTRAN bufferes the downlink data.

Step 814: The SGW sends a bearer setup complete notification to the MME.

In this step, if the SGW determines that the setup of all dedicatedbearers is complete, the bearer setup complete notification message maycarry a parameter to indicate the MME that bearer setup is complete viaa special message or indication parameter; the indication parameter isan indication parameter carried in the bearer setup completenotification and the special message is the bearer setup completenotification. After the MME receives the indication parameter, the MMEmay initiate subsequent operations related to the completion of setup ofall bearers.

Step 815: The MME returns a bearer setup complete notificationacknowledge to the SGW.

After the UE is successfully connected to the target network, the SGWindicates the PDN GW to switch the user plane uplink and downlink datapaths to the E-UTRAN via the PBU or extended PBU message. The indicationmay be sent by the MME or directly by the SGW, or regenerated by theSGW.

FIG. 9 is a flowchart in the third embodiment of the invention wherebearers are set up at a time while the interaction between SGW and PDNGW is based on GTP. As shown in FIG. 9, the process includes:

Step 901: The MME sends a bearer setup message to the SGW, carrying anindication notifying the SGW that a connection setup process of handoveris ongoing.

Step 902: Upon reception of the bearer setup message, the SGW sends aconnect request to the PDN GW.

In this step, if the SGW obtains QoS information of all requestedbearers from the received bearer setup message, the SGW reservesresources for all bearers or else the SGW reserves the default bearerresource; the connect request sent by the SGW to the PDN GW may be aspecial message or carry a special parameter; the message carries a“path not switch” indication or “downlink path switch” indication. Ifthe indication carried in the message is “path not switch”, the PDN GWdoes not switch user plane uplink and downlink data paths upon receptionof the indication but only proceeds to set up bearers; if the indicationcarried in the message is “downlink path switch”, upon reception of theindication, the PDN GW determines that the setup of default anddedicated bearers is not complete in the current E-UTRAN and proceeds toset up bearers.

Step 903: The PDN GW makes an IP-CAN modification interaction with thePCRF. In the process, the PDN GW sends the appropriate IP-CAN Type tothe PCRF and receives the PCC rule delivered by the PCRF.

Step 904: The PDN GW determines to reserve resources for all bearers andsends a connect response to the SGW, carrying information of reservedresources.

In this step, information of the reserved resources includes a series ofTEIDs.

Step 905: The SGW receives the connect response message and sends abearer setup response to the MME.

In this step, the SGW receives the connect response message and if itfinds that it does not reserve enough resources, the SGW reservesresources again according to the information of resources reserved bythe PDN GW carried in the received connect response message and sends abearer setup response message to the MME, carrying information of allresources reserved by the SGW.

Step 906: The MME notifies the E-UTRAN to reserve resources andindicates the E-UTRAN not to set up an air interface connection via amessage or a parameter.

In this step, the message may be a resource reservation message and theindication parameter may be an indication parameter carried in theresource reservation message.

Step 907: The MME sends a bearer update message to the SGW, carryinginformation of the bearers established by the E-UTRAN, including bearersetup success information and bearer setup failure information.

Step 908: The SGW sends a bearer update message to the PDN GW, carryinga downlink data switch indication.

In this step, the SGW receives the bearer update message and if itdetects that the resources it reserves are inconsistent with thosereserved by the PDN GW, the SGW carries information of new resources itreserves in the bearer update message; inconsistency may happen in step902 where the SGW reserves only the default bearer resource.

Upon reception of the message, the PDN GW determines that the setup ofdefault and dedicated bearers of the E-UTRAN is complete. If theparameter carried in step 902 is “downlink path switch”, the PDN GWswitches the user plane downlink data path to the E-UTRAN and maintainsthe user plane uplink data path in the HRPD network.

Step 909: The PDN GW sends a bearer update response to the SGW.

Step 910: The SGW sends a bearer setup complete notification to the MME,indicating the MME that the bearer setup is complete via an indicationparameter or a special message. The indication parameter is anindication parameter carried in the bearer setup complete notificationmessage; the special message is the bearer setup complete notificationmessage.

After the UE is successfully connected to the target network, the SGWuses a special message or indication parameter to indicate the PDN GW toswitch the uplink path maintained in the source network. After thisstep, both the user plane uplink and downlink data paths with respect tothe UE are switched to the target network.

FIG. 10 is a flowchart in the third embodiment of the invention wherebearers are set up one by one while the interaction between SGW and PDNGW is based on GTP. As shown in FIG. 10, the process includes:

Step 1001: The MME sends a bearer setup message to the SGW, carrying anindication notifying the SGW that a connection setup process of handoveris ongoing.

Step 1002: The SGW receives the default bearer setup message, reservesthe resource and sends a connect request to the PDN GW.

In this step, if the SGW obtains QoS information of all requestedbearers from the received bearer setup message, the SGW reservesresources for all bearers or else the SGW reserves the default bearerresource; the connect request sent by the SGW to the PDN GW may be aspecial message or carry a special parameter; the message carries a“path not switch” indication or “downlink path switch” indication. Ifthe indication carried in the message is “path not switch”, the PDN GWdoes not switch user plane uplink and downlink data paths upon receptionof the indication but only proceeds to set up bearers; if the indicationcarried in the message is “downlink path switch”, upon reception of theindication, the PDN GW determines that the setup of default anddedicated bearers is not complete in the current E-UTRAN and proceeds toset up bearers.

Step 1003: The PDN GW interacts with the PCRF to obtain PCC rules of allbearers.

Step 1004: The PDN GW reserves resources for all bearers and sends aconnect response to the SGW, carrying information of the establisheddefault bearer.

Step 1005: The SGW receives the connect response message and sends adefault bearer setup response to the MME.

Step 1006: The MME sets up the default bearer with the E-UTRAN.

Step 1007: The MME sends a bearer update message to the SGW, carryinginformation of the default bearer established by the E-UTRAN.

Step 1008: The SGW returns a bearer update response message to the MME.

Step 1009: The PDN GW sends a dedicated bearer setup message to the SGW.

In this step, if it is necessary to set up multiple dedicated bearers,the PDN GW may set up dedicated bearers in parallel or in series.

Step 1010: The SGW reserves dedicated bearer resources and sends adedicated bearer setup request to the MME, carrying information of theestablished dedicated bearer.

Step 1011: The MME sets up dedicated bearers with the E-UTRAN andindicates the E-UTRAN not to establish an air interface connection.

In this step, the E-UTRAN reserves resources for dedicated bearers andsets up dedicated bearers with the MME. The MME indicates the E-UTRANnot to establish an air interface connection via a message or indicationparameter. The message may be a resource reservation message and theindication parameter may be an indication parameter carried in theresource reservation message.

Step 1012: The E-UTRAN sends a dedicated bearer resource reservationresponse to the MME.

Step 1013: The MME sends a dedicated bearer setup response to the SGW,carrying information of the dedicated bearer established by the E-UTRAN.

Step 1014: The SGW sends a dedicated bearer setup response to the PDNGW, carrying information of the dedicated bearer established by the SGW.

In this step, upon reception of the message, the PDN GW determines thatthe setup of default and dedicated bearers of the E-UTRAN is complete.If the parameter carried in step 1102 is “downlink path switch”, the PDNGW switches the user plane downlink data path to the E-UTRAN andmaintains the user plane uplink data path in the HRPD network.

Step 1015: The PDN GW notifies the SGW that the setup of all bearers iscomplete.

In this step, if the PDN GW determines that the last bearer isestablished, the PDN GW notifies the SGW that the setup of all bearersis complete via a message or indication parameter.

Step 1016: The SGW sends a bearer setup complete notification to the MMEand uses a special message or indication parameter to notify the MMEthat the setup of all bearers is complete. The indication parameter isan indication parameter carried in the bearer setup completenotification. The special message is the bearer setup completenotification. Afterwards, the MME can initiate subsequent operationsrelated to completion of setup of all bearers.

Step 1017: The MME sends a bearer setup complete notificationacknowledge to the SGW.

Step 1018: The SGW sends a bearer setup complete notificationacknowledge to the PDN GW.

After the UE is successfully connected to the target network, the SGWuses a special message or indication parameter to indicate the PDN GW toswitch the uplink data path maintained in the source network.

FOURTH EMBODIMENT

This embodiment describes the assurance of lossless uplink and downlinkdata on the user plane and continuity of services.

Solution 1: The SGW sends a message carrying the path not switchindication to the PDN GW, indicating the PDN GW not to switch the userplane but only to set up the default and/or dedicated bearers.

After the UE is connected to the target network, the SGW indicates thePDN GW again to switch user plane uplink and downlink data paths fromthe source network to the target network.

Solution 2: The SGW sends a message carrying a downlink path switchindication to the PDN GW, indicating the PDN GW to switch the downlinkdata path to the target network when determining the setup of allbearers is complete but maintain the uplink data path in the sourcenetwork; when the UE is connected to the target network, the MME or SGWsends a message or indication parameter to the PDN GW, indicating thePDN GW to switch the uplink data path to the target network. Early pathswitch indications may be generated and transmitted by the MME andforwarded by the SGW, or be generated by the SGW according to thecurrent status and transmitted directly by the SGW.

FIG. 11 is a flowchart in the fourth embodiment of the invention where atarget access gateway indicates an anchor gateway to process user planeuplink and downlink data paths respectively on two user planes. In thisembodiment, the uplink data path in the source network is maintained andthe downlink data path is switched to the target network at thebeginning of handover. As shown in FIG. 11, the process includes:

Step 1101: The UE accesses the target network and handover begins.

In this step, when handover begins, it is necessary to set up data pathsbetween the target access gateway (target AGW) and the anchor GW. Ifcommunications between the target AGW and the anchor GW are based onPMIP, the process proceeds to steps 1102 a and 1103 a; if communicationsbetween the target AGW and the anchor GW are based on GTP, the processgoes to 1102 b and 1103 b.

Step 1102 a: After the target AGW completes the setup of all bearers inthe target network, the target AGW sends a PBU message to the anchor GW.

In this step, the PBU message sent by the target GW carries an uplinkand downlink separation indication. The indication information may beimplemented by extending a flag bit E in the PBU message, with the value1 indicating the necessity to separate uplink and downlink paths and thevalue 0 indicating no necessity to separate uplink and downlink paths.

FIG. 12 is a schematic drawing showing setting of the indicationinformation in the embodiment of the invention. In FIG. 12, the flag bitE is set to indicate whether it is necessary to separate uplink anddownlink paths.

Step 1103 a: The anchor GW sends a PBA message to the target AGW.

Step 1102 b: Before the target network completes the setup of allbearers, the target AGW sends an Activate PDP Context message to theanchor GW, carrying an uplink and downlink separation indication.

Step 1103 b: The anchor GW sends an Activate PDP Context Responsemessage to the target AGW.

Step 1104: The anchor GW separates the user plane uplink and downlinkdata paths.

In this step, the anchor GW maintains the user plane uplink data path inthe source network and switches the user plane downlink data path fromthe source network to the target network.

Step 1105: The remaining steps of handover are completed.

In this step, remaining handover steps include: after the UE is handedover to the target network, the target AGW sends a normal PBU or UpdatePDP Context message, or a PBU or Update PDP Context message that carriesan extended indication parameter to the anchor GW, indicating the anchorGW to switch the user plane uplink data path maintained in the sourcenetwork to the target network, so that both user plane uplink anddownlink paths of the UE are switched to the target network.

FIG. 13 is a flowchart in the fourth embodiment of the invention where atarget access gateway indicates an anchor gateway not to switch userplane uplink and downlink data paths. In this embodiment, the user planeuplink and downlink data paths are maintained in the source network. Asshown in FIG. 13, the process includes:

Step 1301: The UE accesses the target network and handover begins.

In this step, when handover begins, it is necessary to set up data pathsbetween the target access gateway (target AGW) and the anchor GW. Ifcommunications between the target AGW and the anchor GW are based onPMIP, the process proceeds to steps 1302 a and 1303 a; if communicationsbetween the target AGW and the anchor GW are based on GTP, the processgoes to steps 1102 b and 1103 b.

Step 1302 a: After the target AGW completes the setup of all bearers inthe target network, the target AGW sends a PBU message to the anchor GW.

In this step, the PBU message sent by the target GW carries anindication not to switch either the user plane uplink data path or theuser plane downlink data path. The indication information may beimplemented by extending a flag bit N in the PBU message, with the value1 indicating not to switch either the user plane uplink data path or theuser plane downlink data path.

FIG. 14 is another schematic drawing showing setting of the indicationinformation in the embodiment of the invention. In FIG. 14, when set to1, the flag bit N indicates not to switch either the user plane uplinkdata path or the user plane downlink data path.

Step 1303 a: The anchor GW sends a PBA message to the target AGW.

Step 1302 b: Before the target network completes the setup of allbearers, the target AGW sends an Activate PDP Context message to theanchor GW, carrying an indication not to switch either the uplink ordownlink data path.

Step 1303 b: The anchor GW sends an Activate PDP Context Responsemessage to the target AGW.

Step 1304: The anchor GW separates the user plane uplink and downlinkpaths and maintains the user plane uplink and downlink data paths in thesource network.

In practice, when the handover is complete, it is necessary to cancelthe processing of separating user plane uplink and downlink data paths.In the case of PMIP, it is only necessary to send a normal PBU messageto reset the flag bit; in the case of GTP, an Update PDP Context messageis required.

FIFTH EMBODIMENT

In this embodiment, the following technical solution is provided withrespect to the PCC control (such as charging control) during a handoverprocess:

1. An anchor GW interacts with a PCRF to obtain a PCC rule applicable tothe target network. Two sets of PCC rules are available on the anchorGW.

2. The anchor GW enforces the two sets of PCC rules simultaneously,initiates bearer setup to the source network and controls the sourcenetwork and the target network respectively, for example, enforcingcharging control on the source network and target networksimultaneously.

3. When the UE is connected to the target network, the anchor GW deletesthe PCC rule applicable to the source network and then the anchor GWenforces the PCC rule applicable to the target network.

FIG. 15 is a flowchart in the fifth embodiment of the invention wherethe PCEF on an anchor GW controls the PCC rule of the source/targetnetwork during a handover process. In this embodiment, a connectionbetween the SGW and the PDN GW is established before bearer setup. Asshown in FIG. 15, the process includes:

Step 1501: A UE establishes a connection with the target network and thehandover begins.

In this step, a data path is not yet established between the target GWand the anchor GW and the anchor GW may be a PDN GW.

Step 1502: The target AGW sends a bearer setup message to the anchor GW.

Step 1503: The anchor GW interacts with the PCRF.

In this step, the anchor GW initiates an IP-CAN Modification processwith the PCRF to obtain PCC rules applicable to the default anddedicated bearers and the message carries IP-CAN Type information.

Step 1504: The PCEF on the anchor GW receives the PCC rule applicable tothe target network and initiates setup of the target network bearer, andenforces applicable PCC rules with respect to the source network and thetarget network respectively.

Step 1505: The anchor GW initiates setup of default and dedicatedbearers with the target AGW according to the obtained PCC rule.

Step 1506: The UE is successfully connected to the target network.

Step 1507: The PCEF of the anchor GW deletes the PCC rule applicable tothe source network.

In this step, after the UE is connected to the target network, the PCEFof the anchor GW deletes the PCC rule applicable to the source networkand enforces only the PCC rule applicable to the target network.

Step 1508: The remaining steps of handover are completed.

FIG. 16 is another flowchart in the fifth embodiment of the inventionwhere the PCEF on an anchor GW controls the PCC rules of thesource/target network during a handover process. In this embodiment, aconnection between the SGE and the PDN GW is established after bearersetup. As shown in FIG. 16, the process includes:

Step 1601: A UE establishes a connection with the target network andhandover begins.

In this step, a data path is not yet established between the target GWand the anchor GW and the anchor GW may be a PDN GW.

Step 1602: The target AGW sets up default and dedicated bearers with theanchor GW.

Step 1603: The target AGW sends a bearer update message to the anchorGW.

In this step, after the target AGW completes the setup of default anddedicated bearers, the target AGW sends a bearer update message to theanchor GW, requesting setup of a connection.

Step 1604: The PCEF on the anchor GW interacts with the PCRF to obtain aPCC rule applicable to the target network.

Step 1605: The PCEF on the anchor GW enforces PCC rules.

In this step, the PCEF on the anchor GW obtains the PCC rule applicableto the target network and enforces applicable PCC rules with respect tothe source network and the target network respectively. For example, thePCEF performs charging using respective charging rules. This means twosets of PCC rules are available on the anchor node of the network.

Step 1606: The UE is successfully connected to the target network.

Step 1607: The PCEF of the anchor GW deletes the PCC rule applicable tothe source network.

In this step, after the UE is connected to the target network, the PCEFof the anchor GW deletes the PCC rule applicable to the source networkand enforces only the PCC rule applicable to the target network.

Step 1608: The remaining steps of handover are completed.

Through the preceding description of embodiments of the presentinvention, it is understandable to those skilled in the art thatembodiments of the present invention may be implemented by hardware orby software in combination with a necessary hardware platform. Thus, thetechnical solution of the present invention may be made into software.The software may be stored in a non-volatile memory medium (for example,a CD-ROM, a USB disk, and a mobile hard disk), and includes severalindications that indicate a computer device (a personal computer, aserver, or a network device) to execute the methods provided in eachembodiment of the present invention.

Although the present invention has been described through severalexemplary embodiments, the invention is not limited to such embodiments.The sequence number of the embodiments does not represent the preferenceof the embodiments. It is apparent that those skilled in the art canmake various modifications and variations to the invention withoutdeparting from the spirit and scope of the invention. The invention isintended to cover the modifications and variations provided that theyfall in the scope of protection defined by the following claims or theirequivalents.

What is claimed is:
 1. A method for implementing handover, thecomprising: receiving, by a packet data network gateway (PDN GW) of atarget network, a first indication from a serving gateway (SGW) of thetarget network, wherein the first indication is used to instruct the PDNGW of the target network not to switch at least one of a user planeuplink data path and a user plane downlink data path from a sourcenetwork to the target network, after a connection establishing processto the target network via the source network is initiated by a userequipment (UE) when handover preparation is determined in the sourcenetwork; receiving, by the PDN GW of the target network, a secondindication from the SGW of the target network, wherein the secondindication is used to instruct the PDN GW of the target network toswitch the at least one of the user plane uplink data path and the userplane downlink data path from the source network to the target network;and switching, by the PDN GW of the target network, the at least one ofthe user plane uplink data path and the user plane downlink data pathfrom the source network to the target network according to the secondindication.
 2. An apparatus for implementing handover, the apparatuscomprising: a receiver, configured to receive a first indication from aserving gateway (SGW) of the target network, wherein the firstindication is used to instruct the apparatus not to switch at least oneof a user plane uplink data path and a user plane downlink data pathfrom a source network to the target network, after a connectionestablishing process to the target network via the source network isinitiated by a user equipment (UE) when handover preparation isdetermined in the source network; the receiver, configured to receive asecond indication from the SGW of the target network, wherein the secondindication is used to instruct the apparatus to switch the at least oneof the user plane uplink data path and the user plane downlink data pathfrom the source network to the target network; and a processor,configured to switch the at least one of the user plane uplink data pathand the user plane downlink data path from the source network to thetarget network according to the second indication.
 3. An apparatus forimplementing handover, the apparatus comprising: a receiver, configuredto receive a connecting request transmitted from a source network,wherein the connecting request relates to a user equipment (UE); aprocessor, configured to generate an indication in response to theconnecting request, wherein the indication is used to indicate a servinggateway (SGW) of a target network that, when a user plane bearer in thetarget network with respect to the UE is not established, the SGW of thetarget network buffers received downlink data without triggering apaging process with respect to the UE; and a transmitter, configured totransmit the indication to the SGW of the target network.
 4. Theapparatus according to claim 3, wherein the indication is carried in abearer setup message transmitted by the apparatus to the SGW of thetarget network.
 5. The apparatus according to claim 3, wherein theindication is a bearer setup message transmitted by the apparatus to theSGW of the target network, wherein the bearer setup message is used toindicate the SGW of the target network that when the user plane bearerin the target network with respect to the UE is not established the SGWof the target network buffers received downlink data without triggeringthe paging process with respect to the UE.
 6. The apparatus according toclaim 3, wherein the connecting request is transmitted by the UE to thesource network.
 7. A communication system for implementing handover,comprising a mobility management entity (MME) of a target network,wherein the MME is coupled to a serving gateway (SGW) of the targetnetwork in a communicating way and wherein the MME of the target networkis configured to: receive a connecting request transmitted from a sourcenetwork, wherein the connecting request is related to a user equipment(UE); generate an indication in response to the connecting request,wherein the indication is used to indicate the SGW of the target networkthat, when a user plane bearer in the target network with respect to theUE is not established, the SGW of the target network buffers receiveddownlink data without triggering a paging process with respect to theUE; and transmit the indication to the SGW of the target network.
 8. Thesystem according to claim 7, wherein the indication is carried in abearer setup message transmitted by the MME of the target network to theSGW of the target network.
 9. The system according to claim 7, theindication is a bearer setup message transmitted by the MME of thetarget network to the SGW of the target network, wherein the bearersetup message is used to indicate the SGW of the target network thatwhen the user plane bearer in the target network with respect to the UEis not established the SGW of the target network buffers receiveddownlink data without triggering the paging process with respect to theUE.
 10. The system according to claim 7, wherein the connecting requestis transmitted by the UE to the source network